13/671 Pine Ridge Road, Biggera Waters, QLD 4216 Phone: (07) 5594 6824 Fax: (07) 5594 6825

Zinc

What Is It? Zinc plating is the most common, low cost; electroplated coating that is normally applied to ferrous components to give corrosion protection. The coating can be coloured to give gold, silver or blue coatings by post treatment. The relatively low cost, protective nature and attractive appearance of zinc make it a popular coating for nuts, bolts, washers, metal stampings and automotive parts, such as interior components and gas filters. In addition, zinc serves as an effective undercoat for paints when high corrosion performance is required.

What Material Can Be Zinc Plated? Nearly any metal can be zinc plated but the most common are steel and iron on which it offers sacrificial protection.

How Is It Done? The commercial zinc electroplating process has three basic steps:

  • 1. Cleaning the surface, which is normally done in alkaline detergent type solutions, followed by acid treatments to remove any rust or surface scale.
  • 2. Depositing zinc: The work is held on specially designed racks, immersed in a chemical bath containing dissolved zinc and a DC current is applied resulting in zinc being deposited on the work (cathode). Finished Products use alkaline zinc baths, which are more environmentally friendly and produce a more consistent zinc thickness especially in recesses.
  • 3. Post treatment: This provides increased corrosion protection to reduce the corrosion of the deposited zinc. These coating can increase the time to white rust by 10 fold with the yellow giving the best results. Finished Products also apply sealers that are now commonly being specified by the automotive industry that further increase corrosion protection and reduce fingerprinting.

Recommended uses for Zinc electroplating: Zinc plating is used where a clean, smooth, corrosion resistant surface is required. Commonly used on nuts, bolts, metal brackets. etc but it also makes an excellent undercoat for powdercoating or paint. Zinc electroplating can leave recesses on complex shaped components without sufficient zinc coating to provide corrosion protection. Finished Products can recommend other coatings that may overcome this effect.

What Are The Design Consideration For Trouble Free Zinc Electroplating? Don’t design product that will trap chemicals during the zinc plating process. Spot welding, riveted and or assembled parts will cause production concerns Don’t mix metals in the part, stainless steel, zinc or aluminium inserts will cause problems. All parts need to be free rinsing which may require drain holes to be introduced. Try to avoid the use of machined components and black scale-coated steel. Air pockets prevent plating and such areas must be avoided. It is especially accepted that zinc plating provides excellent corrosion resistance in rural atmospheres whereas in marine environments it should be sealed and chromated to provide adequate protection.

What Is The Thickness Of Zinc Electroplating? The Australian specification AS1789-1984 describes four classifications for zinc plating. Service condition 1. is for mild indoor conditions where a thickness of 5?m (micron) is the minimum. For moderate corrosive conditions, 8?m is specified, this makes up the bulk of our business. For severe corrosive conditions 12?m is specified and 25?m is specified for exceptionally severe corrosive conditions. Finished Products can produce to any of these standards.

What Is The Maximum Size Finished Products Can Zinc Electroplate? The Maximum size we can process is 2.8m long by 0.3m wide by 0.8 deep.

Why Are Chromate Conversion Coatings Essential? Zinc as plated is a very reactive metal and rapidly corrodes in air. Chromate Conversions are required to retard this corrosion. Generally Chromate Conversion coatings will retard white corrosion in neutral salt spray as follows:

  • TYPE OF CHROMATE >>>> TIME TO WHITE SALTS ON ZINC PLATE (SALT SPRAY TEST)
  • Clear (bright, blue) >>>> 12-24 hr
  • Iridescent yellow >>>> 100-200 hr